Prorastomus/Pezosiren: when sirenians still had legs

Nothing heretical today.
We haven’t looked at any sirenians yet. And this one adds one more taxon to the LRT.

Figure 1. Prorastomus is a pro-sirenian with legs. All four feet remain unknown.

Figure 1. Prorastomus (or is this Pezosiren) is a pro-sirenian with legs. All four feet remain unknown. Elements from Pezosiren are also shown.

Prorastomus sirenoides (Owen 1855; Middle Eocene, 40 mya; 1.5m in length; Fig. 1) and Pezosiren are basal sirenians with four legs, a short tail and more teeth. They nest with the recenly extinct dugong, Dusisiren, in the large reptile tree (LRT, 1006 taxa).

Figure 2. Sirenian skulls, including Dusisiren, Prorastomus, and Eotheroides.

Figure 2. Sirenian skulls, including Dusisiren, Prorastomus, and Eotheroides. Note the loss of many teeth in Dusisiren.

Compared to its phylogenetic predecessor,
Moeritherium, Prorastomus/Pezosiren demonstrates the reduction in sacral vertebrae, the reduction in the cranial crest and the enlargement of the tail (what little is known). Pezosiren portelli (Domning 2001) is a related genus

According to Domning 2001
“Modern seacows (manatees and dugongs; Mammalia, Sirenia) are completely aquatic, with flipperlike forelimbs and no hindlimbs. Here I describe Eocene fossils from Jamaica that represent nearly the entire skeleton of a new genus and species of sirenian—the most primitive for which extensive postcranial remains are known. This animal was fully capable of locomotion on land, with four well-developed legs, a multivertebral sacrum, and a strong sacroiliac articulation that could support the weight of the body out of water as in land mammals. Aquatic adaptations show, however, that it probably spent most of its time in the water. Its intermediate form thus illustrates the evolutionary transition between terrestrial and aquatic life. Similar to contemporary primitive cetaceans3, it probably swam by spinal extension with simultaneous pelvic paddling, unlike later sirenians and cetaceans, which lost the hindlimbs and enlarged the tail to serve as the main propulsive organ. Together with fossils of later sirenians elsewhere in the world, these new specimens document one of the most marked examples of morphological evolution in the vertebrate fossil record.”

References
Domning DP 2001. The earliest known fully quadrupedal sirenians. Nature. 413 (6856): 625–627. online.
Owen R 1855.
 On the fossil skull of a mammal (Prorastomus sirenoïdes, Owen) from the island of Jamaica. The Quarterly Journal of the Geological Society of London 11:541-543.
Self-Sullivan C 2006. Evolution of the Sirenia.

wiki/Dusisiren
wiki/Prorastomus
wiki/Evolution_of_sirenians
wiki/Pezosiren

Cainotherium: a basal artiodactyl

This one everyone agrees on.
Cainotherium nests at the base of included artiodactyls in the large reptile tree (LRT).

Fig. 1. Cainotherium nests at the base of the Artiodactyla or even-toed ungulates. I wonder if it had five fingers, even if vestiges, given that Ancodus, a derived artiodactyl, retains five fingers.

Fig. 1. Cainotherium nests at the base of the Artiodactyla or even-toed ungulates. I wonder if it had five fingers, even if vestiges, given that Ancodus, a derived artiodactyl, retains five fingers.

Cainotherium renggeri (Bravard 1828, 1835; 30cm in length; Eocene to Early Miocene) was and is considered a rabbit-sized artiodactyl not far from the odd-toed ungulates, like the similarly-sharp-clawed Chalicotherium.

Note that a derived artiodactyl, Ancodus (Fig. 2) had five fingers, so one wonders if Cainotherium likewise had five.

Figure 1. Ancodus nests as a more derived sister to Sus and it retains digit 1 on the manus and pes.

Figure 1. Ancodus nests as a more derived sister to Sus and it retains digit 1 on the manus and pes.

References
Bravard A 1835. Monographie du Cainotherium, Levrault, Paris, 1835.
Heizmann EPJ 1999. Family Cainotheriidae, in : Rössner G.E., Heis- sig K. (éds), The Miocene Land Mammals of Europe, Pfeil, 1999, pp. 217–220.

wiki/Cainotherium

A new set of ancestors for hippos

Updated November 18, 2016 with new data (Fig. 3) on Ocepeia.

Figure 3. Hippopotamus. This stout, wide-faced, fanged mammal does not nest with deer.

Figure 4. Hippopotamus. This stout, wide-faced, fanged mammal does not nest with deer.

The following clears up
another fine mess traditional paleontologists have provided based on taxon exclusion and professional bias. Today, let’s talk about the ancestry of hippos (Fig. 1).

Figure 1. Living hippopotamus. Now I ask you, does this look like a relative to deer and giraffes? Or to mesonychids?

Figure 1. Living hippopotamus. Now I ask you, does this look like a relative to deer and giraffes? Or to mesonychids?

Wikipedia, representing traditonal paleontology, reports
here, The earliest known hippopotamus fossils, belonging to the genus Kenyapotamus in Africa, date to around 16 million years ago. Hippopotamidae are classified along with other even-toed ungulates in the order Artiodactyla. Other artiodactyls include camelscattledeer and pigs, although hippopotamuses are not closely related to these groups.” 

Do you sense the underlying problem here?
They say, hippos are in the Artiodactyla, but not close. This is what is known as a ‘red flag’.

But wait, there’s more! The most recent theory of the origins of Hippopotamidae suggests that hippos and whales shared a common semiaquatic ancestor that branched off from other artiodactyls around 60 million years ago.” 

This is all getting to be completely bogus (based on LRT results)
And very disturbing. Tenrecs are the sisters to whales, as we learned earlier here. But wait, there’s more. “A rough evolutionary lineage can be traced from Eocene and Oligocene species: Anthracotherium and Elomeryx to the Miocene species Merycopotamus and Libycosaurus and the very latest anthracotheres in the PlioceneLook those taxa up. They’re all skinny, long-legged terrestrial grazers. Not hippo-like at all ~

As an example, here’s Anthracotherium….
a big artiodactyl and an anthracothere (Fig. 2). Does it have huge fangs on a wide gape like a hippo? No. It’s just a big old prehistoric deer. Superficially, it does look like a giant tenrec with that long rostrum, but it does not nest with Andrewsarchus, a real giant tenrec.

Figure 2. Anthracotherium and the anthracotheres nest with their long narrow tiny tooth snouts with Ancodus, deer and other gracile artiodactyls, not hippos.

Figure 2. Anthracotherium and the anthracotheres nest with their long narrow tiny tooth snouts with Ancodus, deer and other gracile artiodactyls, not hippos. Whale ancestors do have a long rostrum, but they are hoof-less like tenrecs, not hoofed like ungulates.

Figure 3. Ocepeia: before and after. The original reconstruction is here compared to a tracing of CT scan, duplicated left to right. From the Paleocene, Ocepeia is the current sister to Hippopotamus and mesonychids in the LRT. Already the wide rostrum and high orbit are apparent.

Figure 3. Ocepeia: before and after. The original reconstruction is here compared to a tracing of CT scan, duplicated left to right. From the Paleocene, Ocepeia is the current sister to Hippopotamus and mesonychids in the LRT. Already the wide rostrum and high orbit are apparent.

Here’s how the LRT sees it
Apparently hippos have an ancestry that extends at least into the Paleocene.

Ocepeia daouiensis (Gheerbrant et al 2001, 2014; Paleocene, 60 mya; 9 cm skull length) was considered the oldest known of the ‘Afrotherians’ known from skulls, but the ‘Afrotheria’ is an invalid clade. Gheerbrant et al. 2016 nested Ocepeia with aardvarks and Potamogale, an extant aquatic tenrec. These were all derived from a sister to Arctocyon nesting within the Arctocyonidae. The LRT nested Arctocyon as an omnivorous marsupial.

Here (Fig. 3) Ocepeia is a Paleocene basal to mesonychids like  Mesonyx (Fig. 5; Cope 1872) and Harpagolestes (Fig. 4; Matthew 1909) and also hippos and thereafter anthracobunids, desmostylians and mysticetes (baleen whales). The jaw joint is aligned with the maxillary tooth row. The original reconstruction (Fig. 3, left) differs greatly from tracings made on CT scans (Fig. 3, right) becoming less hippo-like and more mesonychid-like.

The pneumatized skull of Ocepeia
contains many air spaces, even though it is relatively small. Slightly larger skulls have larger canines and so are considered male.

Wikipedia reports, “Mammals are extremely rare in the Ouled Abdoun in contrast to the associated marine vertebrate fauna which includes sea birds, sharks, bony fish, and marine reptiles (including crocodilians, sea turtles, and the sea snake Palaeophis). Terrestrial species were probably transported off shore into the Moroccan sea before fossilization.” Apparently ignored by traditional paleontologists as possible candidates in this formation, hippos and their ancestors, like Ocepeia, could have been aquatic even at that early stage.

Figure 5. Robust Harpagolestes nests between the hippos and Mesonyx.

Figure 4 Robust Harpagolestes nests between the hippos and Mesonyx. Now, doesn’t this look more like a hippo? The LRT agrees with you.

Long known as a robust mesonychid
Harpagolestes makes a good interim taxon between Mesonyx and hippos. Look at hose tusks! Yet it had not yet developed the low, wide skull and elevated orbits that characterize surface dwelling hippos, like Hippopotamus and Ocepeia.

Figure 1. Mesonyx, the first known mesonychid was a sister to Hippopotamus in the large reptile tree. So maybe it was a plant eater.

Figure 5. Mesonyx, the first known mesonychid was a sister to Hippopotamus in the large reptile tree. So maybe it was a plant eater. Now with the addition of Ocepeia and Harpagolestes, it moves a little further away.

We should someday find
mesonychids, like Mesonyx, in Cretaceous strata based on its phylogenetic nesting and the Paleocene placement of Ocepeia.

References
Cope ED 1872. Descriptions of some new Vertebrata from the Bridger Group of the Eocene. Proceedings of the American Philosophical Society 12:460-465.
Gheerbrant E, Sudre J,Iarochene M, Moumni A 2001. First ascertained African “Condylarth” mammals (primitive ungulates: cf. Bulbulodentata and cf. Phenacodonta) from the earliest Ypresian of the Ouled Abdoun Basin, Morocco. Journal of Vertebrate Paleontology. 21(1):107–118.
Gheerbrant E, Amaghzaz M, Bouya B, Goussard F and Letenneur C 2014. Ocepeia (Middle Paleocene of Morocco): The Oldest Skull of an Afrotherian Mammal”. PLoS ONE. 9 (2): e89739.
Gheerbrant E, Filippo A and Schmitt A 2016. Convergence of Afrotherian and Laurasiatherian Ungulate-Like Mammals: First Morphological Evidence from the Paleocene of Morocco”. PLOS ONE. 11 (7): e0157556.
Matthew WD 1909. The Carnivora and Insectivora of the Bridger Basin, middle Eocene. Memoirs of the American Museum of Natural History 9:289-567.
wiki/Harpagolestes
wiki/Ocepeia
wiki/Hippopotamus
wiki/Anthracotherium

A better sister for Astrapotherium: Meniscotherium

Revised Dec 5 2016 with new text and images. 

These are difficult taxa to nest:
The tusks of Astrapotherium (Fig. 1; Burmeister 1879; Hatcher 1902) are canines. The premaxilla is missing. The mandible of Astrapotherium really does stick out quite a bit further than the rostrum.

Figure 1. New interpretation of Astrapotherium skull with premaxilla and large incisor tusks replacing old canine tusks. The canines are absent. That manual digit 1 that Hatcher 1902 did not like in his drawing (Fig. 1 toned beige) is actually a good fit and works in phylogenetic bracketing.

Figure 1. Revised interpretation of Astrapotherium skull with premaxilla absent or transverse and large canines tusks replacing old canine tusks. That manual digit 1 that Hatcher 1902 did not like in his drawing (Fig. 1 toned beige) is actually a good fit and works in phylogenetic bracketing.

Finally a sister!
I didn’t have one really good enough sister taxon for Astrapotherium. Now I do.

Meet Meniscotherium
(Figs. 2, 3; Cope 1874; Williamson and Lucas 1992; Middle Eocene 54-38 mya; 25-50 cm long), which Wikipedia describes as a dog-sized herbivore with hooves found as a pack of individuals.

Cooper et al. 2014 nested Meniscotherium with Phenacodus as a condylarth, a possible member of Afrotheria, perissodactyl. They did not test Astrapotherium.

Wible et al. 2007 nested Meniscotherium close to early cetioartiodactyls (an invalid clade) and close to early Carnivora. They, likewise, did not test Astrapotherium.

The LRT nests the clade of Astrapotherium + Meniscotherium between the clade of Edentates and the clade of Phenacodus.

Figure 2. Meniscotherium skull. In this is a smaller predecessor to Astrapotherium note the genesis of maxillary tusks here and then longer dentary when the teeth are matched to occlude correctly.

Figure 2. Meniscotherium skull. In this is a smaller predecessor to Astrapotherium note the genesis of maxillary tusks here and then longer dentary when the teeth are matched to occlude correctly. Note the lack of contact between the jugal and squamosal.

The retention of five fingers and five toes
is key to the phylogenetic nesting of these taxa. More derived taxa start losing digit 1. We can see the genesis of canine tusks in Meniscotherium.

Figure 3. Meniscortherium skeleton. The fingers and toes are not known. This reconstruction differs from the original in that the pelvis is rotated more vertically.

Figure 3. Meniscortherium skeleton. The fingers and toes are not known. This reconstruction differs from the original in that the pelvis is rotated more vertically. Some specimens were 25 cm long. Others were 50 cm long estimated.

Meniscotherium is the smaller and more plesiomorphic
of the two and is found in earlier strata (Eocene, 50-38 mya) than Astrapotherium (late Oligocene, Middle Miocene, 28-15 mya).

Figure 4. Astrapotherium to scale with two specimens of Meniscotherium.

Figure 4. Astrapotherium to scale with two specimens of Meniscotherium.

References
Burmeister 1879. Description physique de al République Agentine, T. III 1879:517.
Cooper LN, Seiffert ER, Clementz M, Madar SI, Bajpai S, Hussain ST, Thewissen JGM 2014-10-08. Anthracobunids from the Middle Eocene of India and Pakistan Are Stem Perissodactyls. PLoS ONE. 9 (10): e109232. doi:10.1371/journal.pone.0109232. PMID 25295875.
Hatcher JB 1901. Report of the Princeton University Expeditions to Patagonia 1869-1899. Mammalia of the Santa Cruz Beds. IV. Astrapotheria. Scott WB ed. Vol. 6, Paleontology 3. Princeton, NJ Stuttgart 1909-1928.
Wible JR, Rougier GW, Novacek MJ, Asher RJ 2007. Cretaceous eutherians and Laurasian origin for placental mammals near the K/T boundary. Nature 447: 1003–1006. doi: 10.1038/nature05854
Williamson TE, Lucas SG 1992. Meniscotherium (Mammalia, “Condylarthra”) from the Paleocene-Eocene of western North America. Bulletin of the New Mexico Museum of Natural History and Science 1: 1–54.

Hyopsodus: an Eocene pre-dog, not an archaic ungulate

Hyopsodus lepidus (H. paulus type specimen, Leady 1870; AMNH 143783; Eocene; Fig. 1) is traditionally considered an odd-toed ungulate, despite having a five-clawed manus and a four-clawed pes. Wikipedia also promotes this nesting, but unlike most ungulates, they report, “It is believed to have been swift and nimble, living in burrows, and perhaps able to use echolocation,” and it is shown climbing on a tree trunk. Another website lists Hyopsodus as a condyarth.

Here, in the LRT, 
Hyopsodus nests with Canis and more closely with Miacis (Fig. 2), two members of the Carnivora in the large reptile tree (LRT). Shifting Hyopsodus over to the Condylarthra adds nearly 30 steps. Those tiny feet beneath that long and wide body do not look to me like they could be used to excavate burrows or climb trees. Plus that short tail and long torso are not typical of climbing animals.

Figure 1. Hyopsodus as originally reconstructed (below) and as reconstructed here above in two views. This former condylarth now nests with dogs.

Figure 1. Hyopsodus as originally reconstructed (below) and as reconstructed here above in two views. This former condylarth now nests with dogs.

From the Orliac et al. 2012 abstract:
“Hyopsodus presents one of the highest encephalization quotients of archaic ungulates and shows an “advanced version” of the basal ungulate brain pattern, with a mosaic of archaic characters such as large olfactory bulbs, weak ventral expansion of the neopallium, and absence of neopallium fissuration, as well as more specialized ones such as the relative reduction of the cerebellum compared to cerebrum or the enlargement of the inferior colliculus [hearing]. The detailed analysis of the overall morphology of the postcranial skeleton of Hyopsodus indicates a nimble, fast moving animal that likely lived in burrows.” Sounds like a member of the Carnivora…

Figure 1. Miacis, an Eocene ancestor to extant dogs, such as Canis.

Figure 2. Miacis, an Eocene ancestor to extant dogs, such as Canis. Note the transverse premaxilla and tiny premaxillary teeth as in Hyopsodus.

Miacis has long been known as a dog ancestor.
And here it also nests with Canis (Fig. 3). So, compare Miacis to Hyopsodus (Fig. 2) and you’ll find very few differences.

Figure 3. Canis lupus, the wolf that gave rise to extant dogs through selective breeding.

Figure 3. Canis lupus, the wolf that gave rise to extant dogs through selective breeding. Note the five phalanges on the manus and four on the pes.

Several specimens and species are known
of Hyopsodus, most from just teeth and jaws.

References
Orliac MJ, Argot C and Gilissen E 2012. Digital Cranial Endocast of Hyopsodus (Mammalia, “Condylarthra”): A Case of Paleogene Terrestrial Echolocation? PlosOne v.7(2); 2012PMC3277592

Nesting twin-horned Arsinoitherium within the Condylarthra

Figure 1. Famous and enigmatic, Arsinoitherium has been known for over a century, and traditional paleontologists still do not know what it is.

Figure 1. Famous and enigmatic, Arsinoitherium has been known for over a century, and traditional paleontologists still do not know what it is.

FIgure 1. Subset of the large reptile tree, the Condylarthra, featuring Astrapotherium. Note the phylogenetic proximity of Astrapotherium and Tapirus.

FIgure 1. Subset of the large reptile tree, the Condylarthra, featuring Astrapotherium. Note the phylogenetic proximity of Astrapotherium and Tapirus.

Traditionally Arsinoitherium zitteli has been hard to classify.
Wikipedia reports, “Arsinoitherium (Beadnell 1902; Eocene-Oligocene, 36-30mya; 3 m in length; Fig. 1) is related to elephants, sirenians, hyraxes and the extinct desmostylians.” That’s a pretty broad gamut of taxa.

And they’re all wrong according to the large reptile tree (now 812 taxa, subset Fig. 2).

And this came as a surprise to me, too
among 811 other taxa, Arsinoitherium nests with Gobiatherium mirificum (Fig. 3; Osborn and Granger 1932; Middle Eocene), which Wikipedia considers, “one of the last uintatheres” of which Uintatherium is the titular and most famous member. Wikipedia goes on to report, “Gobiatherium lacked knob-like horns, or even fang-like tusks. Instead, it had enlarged cheekbones and an almost spherical snout. Because of the noticeable lack of many diagnostic uintathere features (the horns and tusks), the genus is placed within its own subfamily.” Here’s where tradition and the LRT agree… but let’s push this a little further to see where it takes us within the friendly confines of the current LRT taxon list.

Figure 3. Gobiatherium skull in three views. Though not immediately apparent, Gobiatherium is closest to Arsinoitherium in the LRT.

Figure 3. Gobiatherium skull (A. M. 26624) in three views. Though not immediately apparent, Gobiatherium is closest to Arsinoitherium in the LRT. Image from Osborn and Granger 1932.

Among all tested placental taxa, and despite distinct overall appearances
only Arsinoitherium and Gobiatherium:

  1. redevelop the ascending process of the premaxilla, completely enclosing the naris;
  2. produce a wide, elevated set of nasals, further expanding into horns in Arsinoitherium;
  3. only two molars, rare among placentals;
  4. and no other condylarths have a wide flat cranium, usually a crest or a convex cranium is present.

That premaxillary ascending process
looks so normal. But among marsupial and placental mammals it is very rare indeed! Of course, the LRT does not depend on one or several traits, several dozen nest Arsinoitherium with Gobiatherium and their sisters.

Even without Gobiatherium
Arsinoitherium nests with Uintatherium. Coryphodon nests closer to Uintatherium. All descend from a sister to Thomashuxleya (Fig. 4), which we’ll look at soon in greater detail.

Figure 4. Thomashuxleya is basal to uintatheries and arsionoitheres. It is not a notoungulate, an invalid taxon.

Figure 4. Thomashuxleya is basal to uintatheries and arsionoitheres. It is not a notoungulate, an invalid taxon.

We hold as an ideal
a gradual accumulation of derived traits in derived taxa, like Gobiatherium and Asinoitherium. In this clade, unfortunately we don’t have enough taxa to make that gradual accumulation of traits any more gradual than it currently is. This is the best we can do, at present, with available data and the present taxon list.

But it’s a good start!
And closer than anyone figured out before.

References
Beadnell HGC 1902. A preliminary note on Arsinoitherium zitteli, Beadnell, from the Upper Eocene strata of Egypt. Public Works Ministry, National Printing Department. Cairo: 1–4.
Lucas SG 2001. Gobiatherium (Mammalia: Dinocerata) from the Middle Eocene of Asia: Taxonomy and biochronological Significance. Paläontologische Zeitschrift 74 (4): 591–600.
Osborn HF and Granger W 1932. Coryphodonts and uintatheres from the Mongolian expedition of 1930. American Museum Novitates 552:1-16.

wiki/Arsinoitherium
wiki/Gobiatherium